Thermally responsive device



Feb. 2, 1937. J. A. SPENCER THERMALLY RESPONSIVE DEVICE Filed Nov. 2;1933 FIG. I.

FIG. 3.

FIG. 5.

UNITED STATES PATENT OFFICE THERMALLY RE SPONSIVE DEVIC John A. Spencer,Newtonville, Mass, assignor to General Plate Company, Attleboro, Mass, acorporation of Massachusetts Application November 2 1 Claim.

This invention relates to thermally responsive devices, and with regardto certain more specific features, to such devices which operate uponthe principle of an expanding fluid.

Among the several objects of the invention may be noted the provision ofa thermally responsive device of the class described; moreparticularly,- a device comprising a sealed bulb, capillary tube, andbellows filled with gas, wherein provision is made for a more perfectsealingof the device against leakage of the gas contained therein andwherein the particular materials of construction,

and the gas, are chosen to reduce leakage occasioned by corrosion andthe like; the provision of a device of the class described which,accordingly retains its precise operating characteristics over aconsiderably longer period of utility than prior analogous devicesyandthe provision of a device of the class described which is relativelysimple and economical in construction. Other objects will be in partobvious and in part pointed out hereinafter.

The inventionaccordingly-comprises the elements and combinations ofelements, features of construction, and arrangements of parts, whichwill be exemplified in the structures hereinafter described, and thescope of the application of which will be indicated in the followingclaim.

In the accompanying drawing, in which is illustrated several of variouspossible embodiments of the invention,

Fig. 1 is an elevation, partially in section, of a device embodying thepresent invention;

Fig. 2 is a longitudinal cross-section of the a bulb shown in Fig. 1;

Figures 3 and 4 are fragmentary views of the bulb of Fig. 2 in thecourse of its manufacture;

and,

Fig. 5 isa cross-section similar to Fig. 2 bu illustrating analternative embodiment of the invention.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawing.

For several fields of use, a' thermally responsive device of the presenttype has heretofore beenfound peculiarly adaptable. The customaryconstruction of such a device comprises a flexible bellows chamber, acapillary tube, and a bulb sealed together to form a unit, which isfilled with a .fluid which preferably undergoes a considerable volumechange within the temperature range which it is desired to control.

The bulb of the unit is ordinarily exposed to the temperature of themedium'which it is de 1933, Serial No. 696,344

valves, or the indicating means of a temperature indicating device. I

In such a device, it is'essential that the bellows, capillary tube, andbulb, as well as all joints therebetween, be absolutely tight so thatoperasequent reduction in internal pressure.

Such units have readily been made heretofore 'forthe lower ranges oftemperature in which metals readily soldered or Welded by ordinarymethods can be employed in the construction of the bulb. For moresevereconditions, such as are encountered when the bulb must be exposedin use to the heat and corrosive action of impinging gas flames, unitsmade by heretofore known methods and from heretofore utilized materials,have been found unsuitable. This is because the metal or joints wouldeither become porous, permitting the gradual escaping of the gas, orwould completely melt or burn out at the high temperature or from theeffects of the impinging flame, or would decrease in efficiency becauseof. either a physical or chemical combination or absorption of the gasin the material of the bellows at the high temperatures used.

The present invention provides a thermall responsive device of thisgeneral type which is ideally adapted for use at such high temperatureswithout any of the disadvantages heretofore stated, and whichfurthermore has a low heat capacity in the part of the element exposedto changes of temperature, thus making it unusually quick in itsresponse to temperature changes.

It has been ascertained, as a result of considerable experiment-a1research, that the above disadvantages may be cured if the bulb is 0onstructed of a stainless steel and if thegas employed is argon. Withthese two materials, there is no deterioration of pressure in theresulting device under the said high temperature conditions, nor doesthe bulb itself deteriorate or corrode because of the action of theflame thereon. The particular metals of which the capillary tube andbellows are constructed are not of much consequence, since theseportions of the device are rarely, if ever, subjected to any hightemperatures which bring about the problems that are desired herein tocorrect.

Referring now more particularly to Fig. 1, nu-

tion may not be impaired by leakage and conmeral l indicates a bellowsof customary design.

The material of which this bellows is constituted" may be spring copper;bronze, or anyother material found to be suitable. The end 3 of thebellows l is closed, and comprises the free end ,of the device whichundergoes movement inv operation. The end of the bellows is welded Thegas most preferably employed, as stated i above, is argon.

The construction of the bulb l3 from s'tainless steel is somewhatdifficult. This is because in thefirst place, stainless steel is not aneasy metal to work, and in the second place, because in the thin sheetshere employed (in order to get a quick response to the externaltemperature,

' itis decidedly advantageous that thewalls of the bulb l3 be as thin aspracticable), welding or the ordinary soldering of stainless steel issubstantially impossible. The present invention also includes a methodof manufacturing such a bulb or container by which these disadvantagesare obviated.

.Referring to Figures 2, 3, and 4, it will be seen that the bulb I3comprises primarily a tubular portion l5, which is preferably a lengthof relatively thin seamless stainless steel tubing.

At each end of the tube I5 is formed an inwardly directed annular grooveIT. The ends of the tube I 5 are then closed by inserting stainlesssteel discs l9 and 2! which seat against shoulders provided bytheg'rooves H. The disc I9 is circular in shapeand has no perforationstherein. ,The disc 2| is likewise circular in shape but has a centralopening 23 (Fig. 4), to receive the end of the capillary-tube H. I Afterthe discs I9 and 2! have been placed in position against the shouldersH, the ends of the tube |5 are over-turned or upset or spun as indicatedat numeral 25, and as indicated in dotted lines in Fig. 3,therebyloosely retaining the discs l9 and 2! in position;

The end of the capillary tube -H is next prepared as illustrated in Fig.4, by welding or wiping a bead 21 of cast iron around it near the end.The end of the tube II is then inserted 'into the opening 23 insuch-manner that the bead 21 abuts the disc 21-.

The assembly is next placed in vertical position with the tube II at theupper end, and the various parts at the end of the tube are desirablycleaned and fiuxed'. The end is next filled in an ordinary manner usinga gas welding torch or the like and a cast iron welding rod.

The ultimate appearance of the welded end is f that indicated at numeral29 in Fig. 2.

Using cast iron as a welding material, not only is a secure weldeffected without tinning difiiculties, but also the temperaure requiredis not so great as to burn or melt stainless steel, even though it ispresent in thin sheets. This use of cast iron as a welding material wasdetermined upon only after a considerable amount of unsuccessful.experimentation and constitutes an important feature of this phase ofthe invention. The other end of the bulb I3 is then welded shut in thesame general manner with cast iron. The weld is accomplished more easilyat this end because of the absence of the capillary tube H. 1 Fig. 5illustrates an alternative construction for the bulb I3, in which thelength of tubing of the Fig. 2 embodiment is replaced by a drawn cup 31,also of stainless steel which thus has its end 33 already closed. Inthis case, it is only necessary to make the weld'on the end whichincludes the capillary tube H;

The gas may be introduced into the bulb and bellows unit in thecustomary manner which preferably includes an evacuation of the unitprior to its filling with argon.

In view of the above, it willbe seen that the several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructionsand processes without departing from the scope of the invention,

it is intended that all matter contained in the above description orshown in the accompanying'drawing shall be interpreted as illustrativeand not in a limiting sense.

I claim:

A bulb and bellows type thermally responsive device particularly adaptedfor high temperature control including a bulb formed of stain- ,lesssteeL't-he seams of which are welded with cast iron, and wherein thecontained fluid comprises argon.

JOHN SPENCER.

